1. Field of the Invention
The present invention relates to an audio amplifier switching noise measuring method and device.
2. Discussion of the Related Art
As is known, an important parameter for evaluating audio amplifiers is the noise--also known as "pop"--produced at the load terminals when the amplifier switches from one operating condition to another, e.g. when it is turned on or off, or switched from standby to normal operation and vice versa.
Quality testing the amplifier therefore requires a noise measuring method which:
a) is easy to implement; PA1 b) can be used on automatic test equipment; PA1 c) is fast; PA1 d) is closely related to the sensitivity of the human ear.
Of these, requirements a-c are important for enabling 100% quality control, while d, which is the most important as regards the validity of the test, is also the most difficult to achieve by requiring an objective evaluation of a subjective phenomenon such as a person's hearing.
One method currently used for automatically measuring the switching noise of an amplifier consists in measuring the peak-to-peak value of the output voltage of the amplifier during switching, the measurement normally being made analogically using a peak meter and acquiring the peak to peak value at the end of the transient state. The results of the above known method are often fairly closely related to the sensitivity of the human ear when testing one type of amplifier in the same type of application, but the results are less than satisfactory and differ widely when testing different amplifiers or the same type of amplifier in different applications. This is due to the fact that two transitions with the same peak-to-peak value but a different time pattern cannot be distinguished, even though, to the ear, they may differ widely.
It is an object of the present invention to provide a switching noise measuring method and device capable of providing measurements closely related to the sensitivity of the human ear, and which may be implemented easily on modern test equipment, and applied to any type of amplifier (bridge or single-ended).